Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Assets
Marketable securities - mutual and exchange traded funds	$ 5,574	$ 3,998
Investments at fair value	1,045	1,020
Liabilities
Fair value of warrant liabilities	634	822
Quoted prices in active markets (Level 1) [Member]
Assets
Marketable securities - mutual and exchange traded funds
Investments at fair value
Liabilities
Fair value of warrant liabilities
Significant other observable inputs (Level 2) [Member]
Assets
Marketable securities - mutual and exchange traded funds	5,574	3,998
Investments at fair value
Liabilities
Fair value of warrant liabilities
Significant unobservable inputs (Level 3) [Member]
Assets
Marketable securities - mutual and exchange traded funds
Investments at fair value	1,045	1,020
Liabilities
Fair value of warrant liabilities	$ 634	$ 822